The present invention relates to a power-driven hand tool having a motor-operated drive spindle, adapted to drive a tool which can be fixed on a retaining section of the drive spindle by a securing element, comprising a displacing device that serves to displace the securing element between a releasing position in which the securing element can be released from the drive spindle and a clamping position in which the securing element is clamped on the retaining section by a spring element, the securing element comprising a clamping shaft adapted to be inserted into the securing element, which shaft is axially fixed in the drive shaft in the clamping position, for clamping the tool, and can be detached in the releasing position.
A power-driven hand tool of that kind is known from U.S. Pat. No. 7,344,435 which is fully incorporated by reference herewith.
In the case of the known hand tool, a securing element can be introduced into the drive spindle through a mounting opening of the tool, and can be clamped in the spindle for clamping and fixing the tool on the retaining section of the drive spindle in form-locking engagement.
A clamping device of that kind is adequate for clamping a tool in many applications. However, it has been found that the forces that can be produced by the known clamping device, under the action of high clamping forces, will as a rule not suffice to withstand very high loads of the kind encountered especially in sawing tools and cutting tools with oscillatory drives.
Other clamping devices intended to clamp tools on power-driven hand tools, without the aid of any auxiliary tool, have been known from DE 41 22 320 A1 and EP 0 152 564 B1. The arrangements described by those patents comprise a drive shaft of hollow design, a spindle seated in that shaft and comprising a displacing device and a clamping point formed by a central securing element or a flange that can be clamped on the drive shaft using the displacing device. Form-locking engagement between the securing element and the drive shaft may be provided in this case to prevent the tool from getting detached by braking effects.
However, the described clamping devices are designed exclusively for electric tools with rotary drives. Electric tools with oscillating drives cannot be clamped.